The present invention relates to a halogen-free flame-retardant polyolefin insulation composition and a cable having an insulation layer formed of the same. More particularly, the present invention relates to a halogen-free flame-retardant polyolefin insulation composition which is eco-friendly, can reduce manufacturing costs, has high installation performance and high flame resistance, satisfies properties such as heat resistance, water resistance, an insulating property, cold resistance, etc., and can provide a cable having a high-elongation insulation layer and being thus prevented from cracking or being damaged when bent excessively during installation of the cable, and a cable having an insulation layer formed of the same.
In a cable used for wiring or interior wiring in a general electrical structure or electrical equipment, an insulator is required to have properties such as high heat resistance, flame resistance, water resistance, chemical resistance, an insulating property, cold resistance, and oil resistance in case of fire, flooding, etc.
When a cable for interior wiring for electric light, electrical heating, etc. is installed not to be exposed, the cable is installed by inserting the cable into a specific location, such as a ceiling, a wall, or a floor, and pulling out it from a location spaced a certain distance from the specific location. Here, the cable inserted into the ceiling, the wall, or the floor is transferred using a conduit tube protecting the cable and guiding the cable until the cable is pulled out, e.g., a conduit tube formed of a material such as polyvinyl chloride (PVC).
It may be difficult to transfer the cable using the conduit tube when the cable is excessively flexible or stiff or when the cable is rubbed against an inner wall of the conduit tube or another cable inserted together with the cable. In particular, it may be very difficult to transfer the cable when it is transferred using the conduit tube in a curved region of the ceiling, wall, or floor of a building or facility.
Thus, the cable should have flexibility and stiffness appropriate for the transfer thereof, and a surface friction coefficient of an insulation layer of the cable should be low enough to minimize friction between the cable and either the inner wall of the conduit tube or another cable transferred together with the cable so as to improve the installation performance of the cable. To improve the installation performance of the cable, an installation work may be performed after applying lubricating oil or the like on a surface of the cable. In this case, the oil resistance of the insulation layer of the cable against the lubricating oil should be improved.
A conventional heat-resistant PVC insulation wire used for interior wiring is a wire insulated with PVC resin to which a heat-resistant plasticizer is added. The PVC resin has high heat resistance, high flame resistance, high chemical resistance, high water resistance, and high installation performance but a maximum allowable temperature thereof is relatively low and the PVC resin is harmful to a human body and may cause environmental problems to occur, e.g., it generates toxic gas when it burns. Thus, use of the conventional heat-resistant PVC insulation wire has recently been regulated.
A halogen-free flame-retardant polyolefin insulation cable has been developed and used in place of the conventional heat-resistant PVC insulation wire having the above problems. The halogen-free flame-retardant polyolefin insulation cable is a wire insulated with flame-retardant agent-added halogen-free insulating resin and is eco-friendly since it uses halogen-free insulating resin.
However, even if a flame-retardant agent is added to the halogen-free flame-retardant polyolefin insulation cable to secure flame resistance corresponding to that of conventional PVC resin, the flame resistance of the halogen-free flame-retardant polyolefin insulation cable is insufficient and a surface friction coefficient of an insulation layer thereof is increased due to the added flame-retardant agent. Thus, the installation performance of the halogen-free flame-retardant polyolefin insulation cable is very low. Furthermore, a wire for interior wiring should have a specific color to be differentiated from a cable adjacent thereto. To this end, a certain amount of pigment is added to the insulation layer but the physical properties such as flame resistance of the cable may deteriorate due to the addition of the pigment.
When a large amount of the flame-retardant agent is added to halogen-free polyolefin resin to secure flame resistance corresponding to that of the conventional PVC resin, an elongation rate of the halogen-free flame-retardant polyolefin insulation cable decreases to a large extent. Thus an insulation layer of the cable may have cracks on a surface thereof or be damaged when the cable is excessively bent during installation of the cable.
Furthermore, the halogen-free flame-retardant polyolefin insulation cable is more expensive than the conventional heat-resistant PVC insulation wire. A filler such as an inorganic filler may be added to the insulation layer to reduce manufacturing costs. However, when the inorganic filler is added, the viscosity of an insulation composition increases and thus the content of the flame-retardant agent which is also an inorganic additive should be decreased to secure the extrusion performance of the insulation layer formed of the insulation composition and the yield thereof. Thus, flame resistance may greatly decrease.
If a large amount of an inorganic additive such as the inorganic filler or the flame-retardant agent is added, the additive added into the insulation layer may decompose due to extrusion load when the insulation layer is extruded and thus bubbles may be generated, thereby greatly deteriorating the physical properties of the insulation layer.
Accordingly, there is an urgent need for a halogen-free flame-retardant polyolefin insulation composition which is eco-friendly, can reduce manufacturing costs, has high installation performance and high flame resistance, satisfies properties such as heat resistance, water resistance, an insulating property, cold resistance, etc., and can provide a cable having a high-elongation rate insulation layer and thus being prevented from cracking or being damaged when bent excessively during installation of the cable, and a cable having an insulation layer formed of the same.